Summary: Worn by >40 million people in the USA alone, contact lenses are associated with a risk of sight-threatening infection. With increasing use for myopia prevention and efforts to develop lenses for technological purposes, a surge in lens usage (extended wear specifically) is predicted. Unfortunately, research related to lens-related complications has been hindered by lack of an in vivo model amenable to the many research tools available only for mice. Following a 25-year effort, we have developed a mouse contact lens wear model. This utilizes silicone hydrogel lenses custom made by a contact lens manufacturer to fit mouse eyes, and does not require lid suturing. The lenses enable corneal infection when contaminated with P. aeruginosa, the most common causative agent of contact lens-related keratitis in people. Foundational to understanding contact lens related infection is knowing how a lens impacts the cornea without bacterial inoculation. Preliminary data show the mouse model replicates multiple events occurring during human lens wear, including colonization of the lens with commensal-type bacteria, and a dendritic cell (DC) response within 24 h. Moving beyond what is feasible using human subjects, high resolution time-lapse imaging of mice with fluorescent cell membranes revealed normally not present motile cells resembling neutrophils in the stroma after 6 days of wear. Immunohistochemistry confirmed infiltration of Ly6G+ cells (neutrophil marker). This DC/Ly6G+ response without pathology fits the definition of parainflammation as ?a low-grade inflammatory response at an intermediate state between tissue homeostasis and classic inflammation which can be induced by persistent tissue stress?? The three aims of this project will explore; 1) triggers of parainflammation during contact lens wear, 2) how the signal is transduced within the cornea to drive the Ly6G+ cell response, and 3) its significance during microbe challenge. The hypothesis, based on published and preliminary data, is that parainflammation during contact lens wear in mice can be triggered by microbes colonizing the lens, initiating a sequence of events not otherwise occurring in the normally microbiome-free cornea that function to protect it against commensal-type bacteria, but which primes the cornea to respond overly-aggressively to P. aeruginosa. !